M-Jet 30 - 3D Printable Jet Drive for RC Boats 3D print model

Join the official M-Jet facebook group! https://www.facebook.com/groups/623045356071128

Complete propulsion system for RC Boats.

You get 12 STL files for 12 parts of the jet drive, designed to be FDM 3D printed with no supports. You also get a STEP file of the whole pump, ready to be edited to your needs. You can assemble it and install it into your RC boat.

COMPLETE PDF MANUAL: https://drive.google.com/open?id=10guq2Laz8EfP5fF6TGrs1q0CErPBnrqk

Includes part list, print settings, assembly and installation guide.

M-Jet 30 features:

2-stage configuration, meaning it has 2 impellers and 2 sections of stator vanes. They give the pump better overall handling, consistent performance and instant priming (the delay between the moment when the intake is in contact with water and the moment when it actually starts pumping the water). This is the only way I have found to achieve life-scale jetsprint handling on a RC boat.

Ball steering. It is my new system where the servo is connected directly to a rotating shaft, instead of a pushrod. The advantage of this system is the simplicity - there are only 2 moving parts in total. Therefore, there are also less joints between the moving parts, which reduces the backlash. It uses a rubber O-ring as a seal around the steering shaft instead of a traditional rubber bellow. When you need to do some maintenance, for example change the servo, you only have to loosen the servo coupler and slide the shaft out. The range of movement of the shaft is exactly 60 degrees left and right, so there is no need to set the range of the servo movement on the transmitter.

Integrated ride plate. Many of my previous boats suffered from hopping when achieving higher speeds and this feature has finally solved all these problems. The ride plate lifts the stern of the boat and keeps the bow down, which stops the hopping effect completely. It is adjustable with a single screw - the same way as you would set trim tabs on a prop boat. In addition, it has four blades, which help with sharp cornering and prevent spin-outs. However, if you do not like this feature, you can just uninstall it and never use it.

Integrated watercooling. The water is pushed into a water channel in the Second stage, through a channel in First stage and the Housing, where a silicone tube is connected. Then the cooling loop goes back through the Housing and out of the boat from an outlet. The outlet is angled upwards so that you can control if the cooling works properly.

Integrated removeable intake grate. If your pump sucks grevel and you need to remove it from the impeller, just unscrew one screw and remove the intake grate to be able to access the impeller.

Rear installation.This jet drive is not glued into the hull from the inside like almost all other pumps. Instead, you cut a simple square hole (no difficult circle shapes!) and slide the pump into the hull from the rear. Therefore the thrust force of the pump pushes directly on the stern, instead of pulling the pump away from the glue. This method is much simplier than any other method I have tried. If you are wondering how exactly it works, check the manual listed above.

Performance: The jet drive achieves 3600g thrust at 20000RPM, my motor uses 1200W. However, it is important to understand that static thrust is not the only parameter that determines the performance of the pump: thrust decreases, as speed of your boat increases. Therefore, I also calculate the exhaust velocity using the Thrust equation (Force = mass flow * exhaust velocity). Exhaust velocity is the speed the water leaving the nozzle. Exhaust velocity of this jet drive is 11.9 m/s. The higher the velocity, the smaller the thrust drop at higher boat speed, therefore more top speed. I believe I have found a good balance between thrust and top speed with this pump.

Update 10. 5. 2020: Two parts of the steering assembly, Ball and Servo coupler, were changed for better strength and grip on the steering shaft.

Update 4.11.2020: These parts have been further reinforced.

Update 18.1.2021: The M-Jet was renamed to M-Jet 30.

Update 14.9.2021: A new folder Mods_for_M-Jet_30 was added to the files, including a single blade impeller design mod. It requires more testing on this pump, but was found to dramatically improve efficiency on a different pump.

Update 13.11.2022: The model description was slightly updated.

Update 18.1.2023: STL file for a single stage impeller (to make the pump work without first stage) was added into the mods folder. Steering shaft will not work properly and the impeller hub does not have the correct size, but it can be an interesting experiment for you to test.

Update 3.6.2023: STEP file of the whole pump was added with the M-Jet_30_STEP_file folder.

Update 11.05.2024: Modified parts (housing, ball and servo_coupler) that use threaded inserts instead of inserted M3 nuts were added into the M-Jet 30 folder. Threaded inserts are a preferred option instead of the older nut solution. Thanks to rc3dprinter for suggesting this modification.